The present invention relates to a control system for controlling a differential (slip) limiting force between left and right drive wheels of a vehicle.
A Japanese Patent Provisional Publication No. 62-103227 (Application No. 60-244677) shows one conventional example. A differential limiting force control system of this example is arranged to increase a rate of increase (control gain) of a differential limiting clutch engagement force as a left and right drive wheel speed difference increases to remedy a deficiency in the differential limiting force when the wheel speed difference is great.
However, this conventional control system is disadvantageous for the following reasons. When the control characteristic of the differential limiting force is preset to improve the driving capacity in starting vehicle on a split friction surface or with one drive wheel stuck in a mud, then the differential limiting force tends to be excessive in the high speed range. Therefore, the vehicle stability is poor especially when the vehicle is driven at a high speed on a split friction surface, and the tendency for understeering tendency is too strong especially when the vehicle enters a corner. When, on the other hand, the control characteristic is adapted to improve the stability in high speed driving on a split friction surface, then the driving ability in starting the vehicle on a split friction or rough road surface becomes poor.